I have used the SEM Rock-It Liner on a couple of rigs.
For example, on my sons '66, and this was the first one we did. We sprayed the entire undercarriage with the black, no issues after about 8 years.
On the interior, we used the tintable. We have had a couple of issues where it has separated from the base metal. However, it looks like the couple places this happened are where I had used a metal filler to cover the base metal and fill the crazy multitude of holes in the body. My guess is that I didn't wait long enough for the filer to cure and the off-gassing created a space for it to separate and peel up some.
Would I use it again, absolutely! But I would wait for any filler material to vent/off-gas prior to spraying.
I would also note, the SEM tintable is a white based, vs. black based material. So whatever color you would like the final product to be, the "tint" base must be several shades darker than the end product.
We ended up with 1 gallon of black for the whole bottom of the tub, including wheel wells and up to the front floor break.
The interior required about 1.5 gallons of tintable to cover all the way to the top of the bed sides, floor, behind dash, etc... There are a lot of nooks and crannys that need to be sprayed.
HTH, Joe